The subject invention relates to a continuous process for the formation of polyols. More specifically, the subject invention relates to a continuous process for the formation of sucrose based polyols.
Traditionally, sucrose based polyols have been difficult to form. Sucrose is not very soluble in alkylene oxide solutions, so its use as an initiator for polyol formation has been complex. In addition, sucrose based polyols have generally been formed using the well known batch process in a batch reactor. A batch reactor is a large reactor chamber that includes an agitator and a thermal jacket. The reactants are added in bulk to the reactor under pressure and the reaction proceeds for hours and sometimes days. There are many problems with batch reactors including difficulty in achieving precise control over the composition of the end product. Often the end product displays a range of size distributions. The reaction stoichiometry can be hard to control in a batch reactor. In addition, thermal control can be hard to achieve and the reaction must be run at a common temperature. Finally, the batch reactor needs to be shut down to remove the reaction product, thus slowing production. All of these problems are increased when trying to use sucrose as an initiator because of the very low solubility of sucrose in alkylene oxide solutions.
It would be advantageous to design a continuous reactor assembly to permit the continuous formation of sucrose based high quality polyols. It would be most advantageous to design the reactor assembly in a manner that promotes turbulent or pseudo-turbulent flow of the reactants and that is modular to permit rapid and easy modification of the assembly to meet the design requirements of a variety of sucrose based polyols. It would be additionally beneficial to design the reactor assembly to permit different reaction temperatures at different points in the reaction.
The present invention provides a continuous process for the formation of sucrose based polyols. The produced polyols find particular application as building blocks in the formation of rigid polyurethane foams. The process produces a very high quality polyol.
In one embodiment, the continuous process for the production of sucrose based polyols comprises the steps of continuously forming an aqueous sucrose solution. Continuously flowing the aqueous sucrose solution, a catalyst and an alkylene oxide through a first spiral reaction tube, and substantially completely reacting the alkylene oxide with the aqueous sucrose solution to form a pre-polymer reaction product in the first spiral reaction tube. Continuously flowing the pre-polymer reaction product from the first spiral reaction tube and removing unreacted water from the pre-polymer reaction product. Then, continuously flowing the pre-polymer reaction product minus the water through a second spiral reaction tube and continuously adding additional alkylene oxide to the pre-polymer reaction product, with the alkylene oxide substantially completely reacting with the pre-polymer reaction product in the second spiral reaction tube to form a polyol. In a prefered embodiment the polyol is flowed through additional spiral reaction tubes with alkylene oxide added to each spiral reaction tube to form a final sucrose based polyol having a molecular weight of between 500 to 20,000.